1. Field of the Invention
This invention relates to a boring type mining machine and more particularly to the apparatus for automatically extending and retracting both the cutter bars and the cutter bar extensions by a single actuating means to a preselected position for supporting the cutter chains at the front end of the mining machine.
2. Description of the Prior Art
In boring type mining machines, as illustrated in U.S. Pat. No. 2,890,033, a pair of rotor cutter arms or boring heads are mounted on a pair of parallel positioned drive shafts that extend forwardly from a gear box at the front of the mining machine. Rotation of the drive shafts rotates the rotor arms to cut a pair of parallel bores in a seam of coal or mineral material to dislodge the material from a mine face. A conveyor mounted on the mining machine conveys the dislodged material rearwardly from the mine face for subsequent conveyance of the material out of the mine.
The boring action of the rotor arms leaves upstanding cusps on the floor and depending cusps at the roof. The cusps are cut off by endless chains that are rotated on the machine frame above and below the rotor arms. The chains are rotatably supported at the upper and lower corners of the frame by sprockets and the intermediate portions of the chains are guided within tracks of upper and lower cutter bars. Each cutter bar is retractable on the machine frame together with the sprockets to facilitate movement of the mining machine into and out of position opposite the mine face. Once the mining machine is in position, the cutter bars are vertically extended toward the mine roof and the mine floor respectively. The sprockets move outwardly toward the mine ribs to cut beyond the periphery of the rotor arms in order to dislodge the cusps.
It is the customary arrangement to provide power actuated extension means, such as piston cylinders, to extend and retract the cutter bars. The cutter bars are extended when the machine is in position at the mine face. The cutter bars are retracted to provide clearance at the mine roof and floor and at the mine ribs for maneuvering into a new cutting position or for withdrawing the machine from the mine face.
U.S. Pat. No. 2,890,033 discloses a first pair of piston cylinders for extending and retracting the upper cutter bar and a second pair of piston cylinders for extending and retracting the lower cutter bar. The first and second pairs of piston cylinders move the upper and lower cutter bars independently of the outward movement of the corner sprockets.
As further disclosed in the above patent, each of the corner sprockets that rotatably supports the cutter chains is extended and retracted by individual piston cylinders or jacks. This arrangement requires the careful coordination of the extension of the jacks for the sprockets with the extension of the piston cylinders for the cutter bars so that the the corner sprockets are extended to a position that corresponds to the cutting or working height of the cutter bars. The working height of the cutter bars is determined by the amount of extension of the cutter bar piston cylinders. Thus, once the cutter bars are extended to a selected working height, then each corner sprocket must be subsequently moved individually by the jacks to support the cutter chains at the desired working height.
This operation generally requires a number of adjustments to be made in the position of the corner sprockets to correspond to the position of the cutter bars. If the corner sprockets are not properly positioned relative to the extended cutter bars, the cutter chains will not be correctly positioned in the tracks of the cutter bars or on the chain guides. The chain links are then subjected to excessive wear thereby accelerating the need for repair or replacement. In addition, improper positioning of the corner sprockets relative to the cutter bars can place the cutter chains under excessive tension or generate excessive slack. This not only hastens wear of the chain but substantially reduces the effectiveness of the chains to dislodge the cusps from the mine face.
Therefore, there is need to provide in a boring-type mining machine, apparatus for automatically moving the corner sprockets inwardly and outwardly in response to movement of the cutter bars so that the corner sprockets are correctly positioned for supporting the cutter chains in the desired position as determined by the position of the cutter bars without requiring adjustments in the position of the sprockets after the cutter bars have been moved to a preselected position.